Governor Rick Perry agrees with former Governor George Bush on the proposed law

Both governors argued that current safeguards in Texas are sufficient, and that this bill would give too much power to a judge, to set aside a jury's ruling which declared a prisoner competent enough to be condemned.

However critics say that the existing safeguards do not work and that people who are retarded can still be executed as long as they are not severely impaired.

The US Supreme Court is due to rule on the issue later this year.

Florida Governor Jeb Bush last week signed a bill making Florida the 15th state to ban the execution of retarded defendants; 38 of the 50 states have laws allowing capital punishment

Texas is the country's top death penalty state. Eight people have been executed this year, 247 since 1982.

International criticism

Mr Bush himself was questioned about the policy in an interview with European journalists, before his recent visit to Europe.

He said that no-one who is mentally retarded should be or indeed was executed.

But it was later made clear that he had in mind the kind of system operating in Texas.

The UN High Commissioner for Human Rights, Mary Robinson, has urged him to intervene in several cases, where people with disabilities are awaiting execution in the US.

The problem of such prisoners was highlighted again this week, when a 49-year-old retarded man in Florida was released after spending 29 years in prison for rape and murder. DNA tests have established his innocence.

He is said to have the mental age of eight and to have tried to please police by falsely admitting to the crimes.